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Can a turbo charger be used to increase MPG?

70K views 154 replies 41 participants last post by  tjm73 
#1 ·
I was wondering if MPG could be increased with a properly sized turbo.

Obviously the fuel system would have to be dialed in tightly too, but does anyone have experience with turbo'd 5.0L that have acheived better MPG ?
 
#3 ·
I give the same response to people who ask me if certain BBK parts will improve mileage.

Sure they will since they are increasing efficiency, but that extra power is too much fun to resist....

I was thinking of making the '93 my driver again and getting rd of the '06 (payment) and a turbo 331 '93 Cobra (would need to lower compresion) seems like fun to me.

I was thinking of using a Boost A Pump instead of an FMU with 24# injectors and maybe 8 PSI...

Then again, a turbo 06 GT would be nice too. Gotta love the interior compared to the older cars.
 
#5 ·
ive seen supercharger adds claiming to increase mpg buy like 5-20% and if its true i dont see why a turbo would be any diffrent, if anything maybe even better since its more efficent, but try to keep your foot off the throttle just to hear that turbo spool....its addicting
 
#6 ·
Sure it can yeild substantial improvement in gas mileage. Pull your V8 and put in a turbo 4 cylinder.
 
#8 ·
The power is not completely free. Dyno any car. Now put the turbochargers in with the hotside piping, oil and coolant lines and don't hook up the intake sides. Dyno it again, bet you lose power.

The car will make the same fuel economy when out of boost, and less in boost. A properly sized turbo will not be seeing boost under low and mild throttle application on a street car. Any mpg increase you will get is purely from a better tune.
 
#10 · (Edited)
The car will make the same fuel economy when out of boost, and less in boost. A properly sized turbo will not be seeing boost under low and mild throttle application on a street car. Any mpg increase you will get is purely from a better tune.
x2

The main gas savings of a turbo is at the design stage~ someone deciding to make the car smaller and lighter by using a smaller, lighter 4 cylinder.

As far as installing a turbo on a v8 Mustang as an economy measure... :rolleyes:

FWIW, my three year plan is to install a V2-SQ versus big bore 347. The 347 would be a constant guzzler, whereas the blower "should" get better "quarter-throttle-and-below" mpg's. A 1mpg increase will pay for the blower install!

...in 28 years.

Seriously, going 347 would consume more gas always whereas you get the same performance (or better) with the blower... though under full acceleration the blower uses more fuel.
 
#9 ·
I have noticed a slight increase in MPG with my supercharged Mustangs when cruising down to Fla. and such. Tooling around town though, I can't keep my foot off the gas enough to see an increase. Any increase in power without increase in fuel burn will increase mileage, which is fine with a setup like I have on my Boss Shinda (19# injectors), but my Procharged Saleen has 42#ers and that kills my mileage somewhat. 5% I can see, 20% seems a little far fetched. I suppose I get about 2MPG extra on the interstate when cruising, thanks to the huffer. Incidentally, mufflers and an intake will also help MPG slightly. All in all, a blower/turbo can help MPH as long as you keep of the right pedal, but who wants to do that all the time?
 
#14 ·
imo... if the engine is not 100% (ring seal etc) the turbo would make up for whatever the engine cannot draw on its own. a naturally aspirated engine relies on ring seal to properly draw in air and fuel. with a turbo, it is not as critical. the turbo is always pushing some air, even if not in boost, constantly feeding the engine. i believe you can achieve better fuel mileage with a turbo but i dont think it would be much... unless its a diesel. just my .02.
 
#15 ·
a turbo will NOT increase your MPG. however a turbo car with 400hp will likely have better gas mileage than a 400hp N/A car.

if you are planning to add a turbo to your existing car to increase MPG it's not going to happen. you'll increase hp, and effeciency but not MPG.
 
#16 · (Edited)
Ford is on record as saying smaller engines with turbo's "can" achieve up to a 20% savings over larger NA engines....both making about same HP with turbo model making more TQ. Example....a 250 HP turbo 4 in an Explorer VS a 3.5 V6 (future models) making 260 or so. Or a turbo 3.5 V6 VS a V8. Or Turbo V6 in F150, etc. I also believe Ford was talking about street versions making good TQ and running on 87 with DI. Tuned for TQ and economy.

Anyway...that's what is coming from Ford.
 
#17 ·
A properly matched turbo system can and WILL increase your fuel mileage. How do I know???? I actually speak from experience.

My 85 GT was converted to MAF EFI, and with the stock 302, full 2.5" off road exhaust, stock 3.08 gears, 5 speed, 255lph high flow intank pump and 1.7 roller rockers used to get between 340-350km per tank. That's about 220 miles to a tank, and I never drove miss daisy. This is with a fully functional EFI system and everything hooked up, no smog.

I converted to EFI turbo, with a CRAP C+L maf and 30# injectors. The car NEVER ran right with this maf, and I never got around to changing it. I also never wound up installing the O2 sensors in the system. In this set up, the car used to get between 340-350km per tank. I got the exact same mileage with a 'malfunctioning' and un tuned efi system and through Flowbuster mufflers! My turbo set up had so much more potential, I just used to have a money-vampire GF at the time so she got more spent on her than my true baby (don't give me ####)

On the other hand, my friends 95 GT with GT40 aluminum heads, stock cam, 1.7 rockers, Innovative T61E turbo with a nice custom turbo system, 50lb injectors and 80mm maf, no tune, full exhaust, fully ported Cobra intake and 70mm TB...... he used to get 500km per tank easily (312 miles) and once managed 700km to a tank all highway. That's 437 miles to a tank! I see lots of guys with mild N/A set ups around here talking about 180-220 miles per tank! If you don't get into the boost, it will be more efficient than naturally aspirated. And efficiency is what saves you money.
SS
 
#20 ·
i said it before and i'll say it again. adding a turbo will NOT increase your MPG.

however a turbo car that makes 300hp will likely be more fuel efficient than a NA car that makes 300hp.

read maximum boost by corky bell for those who disagree.
 
#21 ·
Yes,It CAN increase mileage if properly installed/tuned..Ive done quite a few and everyone saw an increase in mileage.unless your just building them for racing then you'll see some improvement.Most problem is that with added HP,Driving habits change.Period.
 
#22 ·
i don't believe it. when you add more air you also have to add more fuel. common sense, and published sources, say that adding a turbo will not increase you fuel efficiency. proper installation and tuning have nothing to do with it.

take a stock 5.0 with 225hp; say it gets 23mpg. add a turbo and the necessary fuel mods that you have to do (bigger fuel pump, 42lb injectors, etc) and now make 350hp. there's NO WAY the turbo car is going to get better gas mileage. NO WAY.

please explain how adding 40-50% more hp can increase mpg?
 
#24 ·
Millhouse,

To me, this is more about the concept of turboing an engine and not about muddying the water with other concepts like changing the cam, decreasing compression ratio, driving more aggressively, or swapping gear and tire sizes. The question being asked here, in my interpretation is, all else equal will will a well-tuned turbocharged setup on a given engine increase overall fuel mileage?

My intuition tells me no. Any time you introduce a restriction in both the exhuast and the intake, I don't see how that would increase fuel economy. Under partial throttle cruise conditions, I don't think that the turbo is pumping air into the cylinder. So, it's not as if the engine is working more easily to pull air in. I think there would be a net decrease in VE.

That said, I'm not entirely sure VE actually plays into fuel mileage. A certain amount of air with a given AFR should produce a constant amount of power all else equal. If you wanted more air, you could just give a little more throttle in an engine with a lower VE. Do the pistons have to work harder? I doubt it. The biggest restriction in the intake path is not the turbo or even the filter, but the throttle body blade. So a high VE intake would need less throttle to move the same amount of air as the less VE intake using more throttle. If the tune is set so that both have the same AFR, then I don't see how we've gained or lost anything on the intake side.

On the exhaust side, there's a big restriction, and it seems clear to me that the motor is going to have to work harder to push exhaust gases through a turbine. This restriction works to the detriment of volumetric efficiency, but more importantly, it's less mechanically efficient. Now, a higher net force is applied to the piston during the exhaust stroke that would otherwise not be present. This would have the effect of requiring more fuel to generate the same net engine output.

In any case, it seems clear to me that thermal efficiency (TE) and Mechanical Efficiency (ME) is more important than VE. There's no doubt that VE is important in power production, but as for fuel economy, adding air and fuel to go the same distance is never going to increase gas mileage. Please don't misinterpret that because making an engine more volumetrically efficient does not mean it will require more air for a given distance. Only that it will need less throttle to move the same amount of air that the engine requires.

I'm not the most articulate person in the world and don't claim to have resolved this dilemma. I'm just trying to get people on the path of thinking through the real physical concepts involved in answering the question rather than making baseless guesses.

Chris
 
#25 ·
Fastdriver, the problem is...gear ratios can have a huge impact on the fuel economy of the setups in question. While simply adding turbo's may not give you any fuel economy change, the optimum gear ratio for a identical naturally aspirated and turbo charged setups have to be taken into consideration....as the original question was in relation to MPG rather than volumetric or thermal efficiency of the engine.
 
#26 ·
It depends entirely on how you do it. Most turbocharged cars aren’t that efficient, partially because they’re typically low compression. This allows for more boost, but the relative efficiency drops by approximately the square root between the low and N/A compression ratios. If you built a high compression engine with a high torque, low rpm cam, gear it for that, and then control the turbocharger correctly, then you could definitely both improve gas mileage and have higher performance than the stock N/A engine.
 
#29 ·
In the sense of turbo vs N/A, take the stock 88 Mustang with a 302, and a Turbo Coupe. For all intensive purposes they make about the same power, one has 4 cylinders, one has 8. I'd say the TC is heavier then the Mustang, but not 100% sure.
The comparison of a turbo to N/A is a tough one. If you're trying to turbo a hobby car, then why are you really worrking about fuel economy...If its a toy/hobby and thats what you are worried about, I'd just stop there because you'll be seriously let down with the amount of money you'll have to spend to have a nice turbo Mustang. Dependent on what your definition of a nice car is....
 
#31 ·
You have to remember....back when this was originally posted, fuel was well past $4/gallon. At those prices, even on a weekend warrior....it matters. I limited myself to only weekend duty....as I have issues with laying off the happy pedal and was burning a hole in my pockets due to fuel prices. If they stay low...I'll sure as hell be driving it occasionally again to work(60miles round trip).
 
#32 ·
Millhouse, it seems like you just blew off everything I said to restate your point. Nevermind, I understand what you're saying, and I agree with you, brother. Higher hp drag oriented cars won't need as much gear, and will therefore be at a lower cruising RPM. Hence, that car will have more fuel economy all else equal.

I won't speak for the OP, but that still does little to satisfy my curiosity about whether adding a turbo itself can increase fuel economy. I won't give a definitive answer on the question, but I will say that I did not notice anything impressive in the way of gas mileage in my old twin-turbo. I don't *think* it did as well as my old n/a 302, but it was also a heavier car by about 250 lbs with a different cam and induction package. I'll let you know how the new combo works out, but I have no point of reference to compare it to since I'll never drive it n/a.

So, I'm left without any good reference point.

What I can say is that there are some in this thread arguing their hearts out and getting defensive. Nevertheless, they are off base. Turbocharged vehicles under any boost do not make more hp with less fuel. If you don't believe me, research the term "brake specific fuel consumption" and find average values applied to n/a, supercharged, and turbo-charged engines. N/A has the lowest BSFC every time. Also, the engine will always "suck" air in at cruise, unless you're going up a steep incline or are under an abnormally heavy load. Whether turboed or not, at a normal cruise, the turbo will not produce positive boost in the manifold - there will still be a vacuum.
 
#36 · (Edited)
Keeping rpm constant, obviously, intake boost won’t accomplish anything since fuel efficiency would be determined by the lack of cylinder filling, so what ever boost was attained would have to be negated by the throttle body position. The gain would have to come from the exhaust side, specifically, intake contamination.

As an example, keeping the cylinder filling from the intake now constant also and looking at the power produced, let’s say that the cylinder is filled 25%. The work needed is a function of compressing that 25%, the work generated, given a 4x Kelvin rise in heat after ignition would be four times that, we’ll call it a net work output of (4-1) =3. Now let’s say that the restriction on the exhaust side leaves some exhaust in the cylinder, filling another 25% of that cylinder, the work of the compression then doubles, but the work generated also increases, since both pressures have increased. The net result on the positive work side would be that the final temperature would be lower, while the pressure would be slightly higher:

The relative work then needed would equal 2, the relative work output would equal 5, giving the same amount of net work, but some of the heat would be absorbed by the remaining exhaust charge in lieu of the cylinder and head. So the net result, since there is a lower temperature differential between the gas and it's surroundings, would be that the heat would be used for expansion of the exhaust gas instead of heating the engine. Unlike an egr system, which also increases mileage, the restriction of exhaust gasses would also suffer less from dilution, since the egr system is fed through the intake system while the exhaust restriction happens in the cylinder itself.

Obviously, this is over simplified, the work of compression and expansion have to be integrated, there is no consideration of the heat of compression or the differences in heat between the exhaust and intake temperatures. It also assumes that the restriction in the exhaust causes a significant amount to be left in the cylinder when compared to having no restriction. But it does provide a viable theory that the intake contamination could cause a decrease of the heat loss from the system, which would make it more efficient, at least in theory.

I think the reality though is that the gains shown on the tc cars is more a function of cam timing and other modifications
 
#33 ·
So all of us building the turbo cars out there today and seeing increased MPG are just really being brainwashed by aliens..WE really ARENT seeing MPG drop.Its all a hoax..:rofl:
Bestowed upon us by "the man" Or wait,wait,Our calculators just Start malfuntioning as soon as We install the turbos..We can no longer figure out an average MPG.Yea,Thats GOTTA be it,No other feasible explanation..Guess the tune messes with calculators ability to divide..:rolleyes:
 
#34 ·
I'm kinda late in the thread,
Lets not forget to factor in VE ( volumetric efficiency ) either when in terms of boosting. You can have a turbo four banger like say a EVO 8 and actually get LESS mileage. Then say my good buddies 99 N/A Cobra. They aregueably make about the same power. They weigh within a few pounds of one another as well. I know from experience that once you modify and tune the car. ONTOP of driving like you have commonsense since that it is possible. I think the expression is "Have your cake and eat it too". So I think this is what the original poster was thinking when he made the question. IMO if you maximize what the car does already to do more efficiently. It will in a since get better mileage. If you're asking by simply "slapping" a turbo on there and then expecting it get just simply get better mileage. It doesn't quite work like that at all I'm afraid. - to an extend
 
#35 ·
I would love to see your test data 96tangcobra. And, if your post was directed at me, then you must've missed the part where I stated that I don't know the answer to the question.

Nevertheless, what I posted about cruise vacuum and BSFC is not a guess, it's fact. If you insist, I will even find and post links to demonstrate my points. If your post wasn't directed at me, then disregard.

Chris
 
#42 ·
Test date as in the pieces of paper That we all write down mileage on to calculate how may miles we just drove on X amount of gas?Sure,I can get those all day long.We'll just put it this way,There are AT LEAST as many links out there that have shown peoples personal vehicles (That actually own/drive them) and getting as good or better gas mileage than there are posts put up by people that say it its not possible that dont have a clue how they work or because they have never had/built/driven one..
 
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